应能动学院王秋旺教授邀请，美国Old Dominion University（欧道明大学）Thomas B. Gatski教授将于2016年9月29日来访交流并做学术报告，欢迎大家积极参加。
Thomas B. Gatski教授于1976年毕业于宾夕法尼亚州立大学，获博士学位。后在布朗大学进行博士后研究，现任美国Old Dominion University（欧道明大学）海洋、地球及大气科学系教授。主要研究领域包括：湍流剪切流研究、气动表面减阻机理、湍流数值模拟等。编著4本湍流及转捩相关的书籍，近年来担任过International Journal of Heat and Fluid Flow主编、ASME Journal of Fluids Engineering和Theoretical and Computational Fluid Dynamics等期刊编委。
报告时间：2016年9月29日（周四）下午15:00-16:30
报告地点：东三楼东汽报告厅
报告题目：ANALYSIS AND PREDICTION OF TURBULENT VISCOELASTIC FLOWS
报告摘要：
It has been well-known for over six decades that the addition of minute amounts of long polymer chains to organic solvents, or water, can lead to significant turbulent drag reduction. However, it has only been the last twenty-five years that the full utilization of direct numerical simulation of such turbulent viscoelastic flows has been achieved. The unique characteristics of viscoelastic fluid flow are dictated by the nonlinear differential relationship between the flow strain rate field and the extra-stress induced by the additive polymer. Some basic features of such constitutive relationships are presented that delineate among the various types of non-Newtonian and viscoelastic fluids.
A primary motivation for the analysis of these turbulent fluid flows is the understanding of the effect on the dynamic transfer of energy in the turbulent flow due to the presence of the extra-stress field induced by the presence of the viscoelastic polymer chain. Such analyses utilize direct simulation data of fully developed channel flow for the FENE-P (FiniteExtendableNonlinearElastic –Peterlin approximation) fluid model, and results at a moderately high friction Reynolds number of order 103at both medium (30%) and high (58%) drag reduction levels are presented. The transfer of energy is analyzed in physical space through a sequence of energetic budgets that include the mean and turbulent kinetic energy, and the mean polymeric and elastic potential energies. For channel flow in spectral space, a two-dimensional spectrum is formed with a spatial dependency in the wall-normal direction. In addition to allowing for an assessment of energetic content over a broad spectral range, it also allows for an assessment of energetic interchange within the plane of shear. It is shown that the primary effect of the interaction between the turbulent and polymeric fields is to transfer energy from the turbulence to the polymer, and that the magnitude of this transfer does not change between the low and high drag reduction flows.
As with the turbulent flow of a Newtonian fluid, the traditional approach of Reynolds-averaged Navier-Stokes (RANS) model development can be extended to the turbulent flow of a viscoelastic fluid. Such models require some form of closure of the extra-stress contribution of the viscoelastic fluid to the turbulence dynamics. Such approaches are relatively new and have been primarily based on phenomenological extensions of the Newtonian fluid models
